Two Things I Really Like About ITG2

The average song length is about 2 minutes, or 30% more than PIU or DDR's.

Some Double steps make one step wide (i.e. spread legs wider apart) and fast; from the physical exercise POV, it requires broader ROM (range of motion) in the same amount of time.  In other words, it requires faster and more powerful moves.  Reactor and Habanera 1 (both on Double Expert) are two fine examples.

Note, however, one must not use the bar in order to take advantage of this.  The bar helps one move the center of mass around the center of the platform and reduce the range of movement (on the pad).  While it helps passing some of the harder songs (especially level 11 and above), it reduces the ROM required for moving rapidly between 1P and 2P.